The present invention relates in general to motion control systems and in particular to incremental motion control systems.
In servo control systems or incremental motion systems such as the one described and claimed in U.S. Ser. No. 804,553 entitled "Servo Control System" filed in June, 1977 by Jacob Tal and having a common assignee as the subject application, it is necessary to controllably move a load such as the lens system or shuttle of a camera back to a first position after following a moving object field and lock the load in this position. In a document processing system such as the one described in U.S. Ser. No. 723,361, entitled "Document Photography Sytem", and having a common assignee as the subject application, the return to the first position and its locking therein must be accomplished very quickly in order to film documents which vary from 4.875 to 9.25 inches in length, and which move at a rate of 100 inches per second to thereby process up to 600 documents per minute. The subject application describes and claims improvements over the Jacob Tal application in the return home circuit, the home lock circuit, the controller and position sensors, and the relationships therebetween to provide even greater speed and accuracy in returning and locking the load in its first or home position. The present invention's nearly all digital circuitry avoids many of the problems inherent in an analog system, such as frequent adjustments of amplifiers to compensate for variations in temperature and power supply voltage.
Also, the subject invention includes a method and apparatus for locking the servo system on the edge of a timing disk as opposed to locking on a slot in the timing disk as shown in the Jacob Tal application. Therefore, precise mechanical adjustment need not be made to sense the slot but rather the position sensor can be fixedly positioned so as to sense only the edge of the timing disk. As a result, the return movement of the timing disk is not only quickly affected, but also, the timing disk is very accurately locked into position in readiment to track or follow a second document.
The apparatus of the subject invention controllably moves a load in a return mode back to a first position after being moved towards a second position by a forward control circuit. The load is moved from the first position in a forward mode by a motor to track a moving object field. The load has a displacement resulting from moving from the first position towards the second position. The apparatus, constructed in accordance with the instant invention, comprises a sensing means for sensing the displacement of the load by generating a feedback signal at predetermined intervals along the displacement in both of the forward and return modes. Detecting means detect the passage of the moving object field to provide a return signal after the object field has passed a predetermined position. A driving means controllably moves to load back towards the first position in the return mode in response to the return signal. The driving means includes the motor for supplying the moving force. The motor moves the load to the second position in the return mode after responding to the return signal to define an overshoot displacement. A return home circuit means is responsive to the difference in the number of feedback signals in the forward mode and the current number of feedback signals in the return mode for providing an energizing bias signal to the driving means to cause the driving means to move the load back to the first position.